There are many occasions within a can manufacturing plant in which a mass of containers needs to be fed into a single line or multiple single lines for supplying the containers to, decorators, base coaters and other apparatus in the plant which must perform an operation on or with respect to the container. As the development of higher speed apparatus for performing all these functions is developed, it becomes necessary to develop apparatus for providing the containers to the equipment at greater speeds. Until fairly recently, single filing was done by a variety of mechanical single filers. However, more recently a significant breakthrough in the handling of containers occurred with the development of air conveyors and single filing devices which support the containers on a layer of air and use air as a propelling force for manipulating and moving the containers.
One such single filing apparatus is disclosed in my U.S. Pat. No. 4,462,720 for "Air Table System" which issued on July 31, 1984. In this device, the containers are supported on a table by a layer of air provided by air jets slanted in the downstream direction toward a single file conveying zone. An imperforate cover is placed above the surface of the table a distance slightly greater than the longitudinal dimension of the objects being transported and is positioned over at least a portion of the single file conveying zone. Blow-back jets are connected to a source of air under pressure for supplying air in the single file conveying zone in opposition to the direction of normal flow of the object. By the use of this apparatus, a mass of containers can be rearranged into a single file arrangement for discharge at the downstream end of the table.
Another single filer is shown in my U.S. Pat. No. 4,561,806 for "Vertical Single Filer Conveyor System" which was granted Dec. 31, 1985. In this apparatus, the containers are fed from a mass onto a table which has at least three zones extending from an upstream location. The containers are supported and moved by a prearranged pattern of flotation air jets. In addition, a row of acceleration jets, which are larger in size than the flotation jets, are located in the table adjacent to and spaced in parallel relation to converging sides of the table to form two converging rows of acceleration jets. Means is provided to incrementally increase the volume and velocity of air through the acceleration jets between each of the three zones from the upstream location to the downstream location to accelerate and longitudinally separate the objects as they move along the table from the upstream location to the downstream location so that the converging of the sides coacts with the acceleration jets to converge the longitudinally separated objects in a prearranged pattern to bring them into single file. This device has been found to be very satisfactory for placing smooth decorated cans in single file at relatively high speeds.
Neither of these devices will work with highly etched containers. During the manufacturing process, the containers are run through an acid wash which etches the outer surface of the containers so that the decorative coating will adhere to the surface of the container. Furthermore, because of environmental concerns, the acid cannot now freely be dumped and therefore it is impossible to control the amount of etching on the cans as was previously possible. In other words, the acid solution must be strong enough to provide the minimum etching required but if there is a stall in the line and the container stays in the etching solution too long, the acid cannot be dumped but rather the container just becomes more highly etched. This creates great problems in manipulating the containers because the adjacent contacting edges of the etched containers act like little gear teeth and interlock with each other so that the containers want to rotate with each other rather than moving individually and sliding past each other.